Unformatted text preview: Part (c): To get two students in the same class and another in a di±erent class, we must Frst pick the class from which to draw the two students from. This can be done in ± 3 1 ² = 3 ways. Next we pick the other class from which to draw the singleton student from. Since there are two possible classes to select this student from this can be done in two ways. Once both of these classes are selected we pick the individual two and one students from their respective classes in ± n 2 ² and ± n 1 ² ways respectively. Thus in total we have 3 · 2 · ± n 2 ²± n 1 ² = 6 n n ( n1) 2 = 3 n 2 ( n1) , ways. Part (d): Three students (all from a di±erent class) can be picked in ± n 1 ² 3 = n 3 ways. Part (e): As an identity we have then that ± 3 n 3 ² = 3 ± n 3 ² + 3 n 2 ( n1) + n 3 ....
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 Winter '08
 G.JOGESHBABU
 Probability, Numerical digit, ways

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